1. Field of the Invention
The present invention relates to a content playback technique which uses digital content and, particularly, to a content playback technique capable of securely (that is, while protecting the copyright) using content, such as music and video, having a predetermined use right, including the copyright, by a content creator.
More particularly, the present invention relates to a content playback technique for performing copyright protection by permitting use of encrypted content by using a token and, particularly, to a content playback technique capable of sharing content among plural users having a token of encrypted content.
2. Description of the Related Art
A copyright is a relative, exclusive right capable of using authored material and is contained in one of commonly called “intangible property rights”. The “authored material” referred to herein is one in which thoughts or feelings are expressed in a creative manner and refers to one which belongs to the fields of the arts, sciences, fine arts, or music. A copyright is protected by, for example, copyright acts by individual countries and by international treaties such as the Berne Convention and the Universal Copyright Convention.
It is quite rare for a copyright to be used by the copyright owner himself, and it is usual for the copyright owner to obtain a fixed amount of payment for the use of the copyright by another person, and consents to the use of the copyright. For example, a record company having copyrights on music content such as musical pieces can demand copyright royalties corresponding to the number of times the content is used, with respect to a broadcasting station which uses, that is, broadcasts, music content and with respect to content distribution dealers.
In recent years, information processing and information communication technologies have made rapid progress, and internationalization has advanced remarkably in the cultural and economical fields. In such a social environment, the situation concerning copyrights is constantly changing. It is said that the history of copyright protection dates from the invention of printing technology at around the middle of the fifteenth century. At the present time, all data and content are being digitized, so that they can be handled on computer systems, and as a consequence of this, distribution of authored material and the form of sale have been transformed, and duplication of copyrighted material is becoming progressively easier. Therefore, it is considered to be necessary to assist authorized use of copyrighted material or to eliminate unauthorized use thereof from the viewpoint of information technology, and to expand the protection of copyrights.
For example, conventionally, distribution and sale of music content are performed solely by displaying physical media, such as record discs and CDs (Compact Discs), on sale in a store via physical distribution channels and the market. However, recently, distribution and sale forms are becoming popular such that music content as digital data is provided on a Web site such as on a WWW (World Wide Web) server, that is, music content is distributed in a public network environment such as the Internet. In the content distribution action of the latter case, the presence of physical media and physical distribution, and sale channels are completely omitted. That is, almost no physical limitation conditions are imposed, and each ordinary user can freely obtain content.
For example, a terminal on the street for digital content sale can be disposed in a public place such as a convenience store, so that a user can download, that is, purchase, music content at that place. Alternatively, the user himself can download music data from the user's home through a telephone line. Furthermore, as a result of the expansion of a mobile environment, it has become possible to download music content at a desired place at a desired time period by using the line of a portable telephone.
Recently, portable information apparatuses called “multi-functional portable terminals” have appeared. This type of portable apparatus has not only a portable telephone function and an Internet access function so as to download music content, but also has a music content playback function and an apparatus-to-apparatus wireless communication function for transferring data and content to another neighboring apparatus. For the apparatus-to-apparatus wireless communication function, for example, a short-distance wireless communication technique, such as “bluetooth”, can be used.
In the conventional distribution and sale of music content via physical media, the purchase action of storage media is almost equivalent to the consent of use of the authored material. In contrast, when distribution and sale are performed in the form of digital content, since duplication becomes even easier, it is necessary to curb and crack down on duplication of authored material and illicit use from a technical point of view.
The copyright protection of music content is realized by using, for example, one type of license key called a “token”. The protection of music content using a token is broadly realized by the procedure such as that described below:    (1) Music content is distributed in an encrypted form.    (2) A secret key for the encrypted music content is used as a token.    (3) The token is supplied to only a content playback apparatus of an authorized user through a path in which security is ensured.    (4) Inside the content playback apparatus of the authorized user, the token is stored in a circuit module having a tamper-resistant characteristic, and the token is used to decrypt the encrypted music content. It is preferable that, in addition to a token, program codes which play back content using a token be executed within a circuit module having a tamper-resistant characteristic.
As a result, decrypted use of music content is permitted by being limited to the authorized use time in the playback apparatus of the authorized user. The “tamper-resistant characteristic” means the properties of a circuit package such that the circuit package is sealed strongly, and when an attempt to disassemble the circuit package is made so as to decrypt the internal data, the circuit itself is broken, and internal access is inevitably prohibited.
In the conventional forms of music content sale, possession of content media is a proof of being an authorized user. In contrast, when distribution and sale are performed in the form of digital content, obtaining a token rather than content is a proof of being an authorized user. In the latter case, for example, if only a token is possessed in a multi-functional portable terminal, it is possible to obtain music content via a network at any time and to play it back. That is, the music content and the token can be separated from each other and be used, and physical media need not always be carried. As a natural consequence, problems specific to handling of articles, such as breakage and loss of media, can be resolved.
However, since a token is always required to play back music content, there are several problems from the viewpoint of managing tokens.
For example, in a case where it is desired to play back music content by two or more apparatuses, conventionally, it is only required to move or replace physical media among the apparatuses. However, in the case of encrypted content, a token must be moved among the apparatuses.
In a case where free duplication of a token is admitted among apparatuses, content playback is possible at both apparatuses of the duplication source and the duplication destination, and this is convenient. However, it becomes difficult to crack down on unauthorized duplication of tokens, and copyright protection for content becomes insufficient. Furthermore, when movement of a token is permitted among apparatuses in a form in which duplication is not allowed, the copyright protection is ensured, but when the apparatuses become separated, leaving behind of the token becomes a problem. In the original apparatus in which collection of the token has failed, even if the apparatus has the encrypted music content itself, the apparatus cannot play it back. Leaving behind of the token is almost equivalent to the leaving behind of the medium.
Furthermore, in a case where plural users bring tokens and authorized playback apparatuses and enjoy content playback in a state in which the tokens are concentrated in a single apparatus, when each user disperses, there is a risk in that incorrect taking of the tokens may occur. Such incorrect taking of tokens is theoretically almost equivalent to the incorrect taking of the media.
Here, a specific example is considered.
For example, in the Dec. 13, 1999 issue (n. 759) of Nikkei Electronics, pp. 139-150, a proposal is described such that “bluetooth” (described above) as a short-distance wireless data communication technique is used in a LAN (Local Area Network) inside a vehicle. In such a case, a hands-free environment can be constructed easily by integrating the portable apparatus carried by each occupant and the vehicle-mounted audio apparatus by using a wireless LAN. That is, by specifying the output target of the music content possessed by each portable apparatus to the vehicle-mounted audio apparatus, each occupant can bring music content which can usually be listened to only by one person into the vehicle and to share the playback thereof without head sets. The “portable apparatus” referred to herein may be the above-mentioned multi-functional portable terminal.
Also in such a use form, the vehicle-mounted audio apparatus which plays back music content must have a corresponding token.
For example, in all the portable apparatuses, by moving the tokens, together with the music contents, to the vehicle-mounted audio apparatus, centralized management of the music contents possessed by all the occupants can be performed at one place, which is convenient. It is possible for each occupant to receive a list of music titles collected by the vehicle-mounted audio apparatus via a wireless LAN and to freely select the musical pieces provided from another occupant. Furthermore, since the storage capacity of the vehicle-mounted audio apparatus can be made larger than that of the portable apparatus, it is convenient to store a large number of music contents in a centralized manner. In addition, it is possible for each occupant to share a variety of audio functions of the vehicle-mounted audio apparatus. In general, the vehicle-mounted audio apparatus is more expensive than the multi-functional portable terminal and can provide higher sound quality.
However, in order to ensure the copyright protection for each content, a token must be moved in a form in which unauthorized duplication, and illicit use and diversion are prohibited and, furthermore, the token must be collected again in each original portable apparatus. It is difficult to realize such token movement and collection by an intuitive operation.
Furthermore, when plural users collect tokens, there is a risk that troubles, such as leaving behind/forgetting to put back, incorrect taking, loss, etc., of tokens, may occur. Even if the “stray” token appears, in order to reserve the content use right of the original owner, it is not permitted for the vehicle-mounted audio apparatus side to delete or discard the token freely.
On the other hand, as a method of sharing music content inside the vehicle without moving the tokens, a case can be conceived in which data played back by the original portable apparatus is transmitted to the vehicle-mounted audio apparatus in real time by using a wireless LAN, and sound is output from the audio apparatus. According to this method, since the token stays in the original portable apparatus, the operations, that is, token management, can be greatly simplified.
However, since all the music contents are not centralized in the vehicle-mounted audio apparatus, the music content possessed by an occupant cannot be freely selected by another occupant. Furthermore, while content playback is being performed, since the portable apparatus is at a fully operating state, power consumption is increased (generally, the portable apparatus is battery-driven, and an increase in the power consumption is serious). Furthermore, from a theoretical point of view, since it is merely that line-out output is made from the portable apparatus and the vehicle-mounted audio apparatus is used simply as an audio amplifier, it is not possible to enjoy a variety of audio functions of the vehicle-mounted audio apparatus.